Oil sand containing bitumen mined from the ground is generally slurried with water as part of an initial process for eventually removing the bitumen from the oil sand. Oil sand is a type of bitumen deposit typically containing sand, water and bitumen. When the oil sand deposit is located relatively close below the ground surface, the oil sand is often extracted from the deposit by excavating down through the ground surface to where the oil sand deposit occurs and removing oil sand from the deposit with heavy machinery.
Typically, this removal of the oil sand from the deposit is done with large power shovels and dump trucks, with the power shovels removing shovel-loads of oil sand from the deposit and loading the collected oil sand into dump trucks, which load the oil sand onto conveyors to be carried away for further processing.
Tramp metal inclusions in mined oil sand may pose a problem in slurry preparation methods, particularly in screen-less slurry preparation towers. Tramp metal is often a piece of metal from machinery used earlier in the process, such as a piece of shovel tooth from the power shovel or a piece of crusher tooth from the primary crusher. Large pieces of tramp metal may damage or jam one of the roll crushers used in the slurry preparation tower when it is fed into the slurry preparation tower along with a portion of oil sand. This may result in the entire process being stopped while the crusher rolls are either repaired or the jam is located and the tramp metal removed. This may lead to lengthy outages to remove the object from the crusher rolls and affect repairs if any damage has occurred.
Screening processes typically remove tramp metal through the screening apparatus, however, with screen-less slurry preparation processes, it may be desirable to detect and remove the tramp metal prior to crushing in the slurry preparation tower to avoid such outages.
Many metal detection methods are well known. Magnetic pulse induction methods are typically used for detecting metal objects because it generates a strong signal, and both ferrous and non-ferrous metals can be discriminated. Typically this method first generates a large magnetic pulse, and then measures the decay of magnetic fields generated by currents induced in metal objects by the first pulse. Various techniques, including balanced coils, are often used to cancel out the background signal so only changes are detected. In environments containing a significant amount of metal, background noise from that metal is a large component of the detected signal and background subtraction is less effective as the desired signal becomes lost in the noise. This is especially true in industrial environments where background metal may vibrate, or change configuration.